A high frequency semiconductor device, such as a microwave amplifier, provides a circuit substrate for mounting active elements such as transistors, passive elements such as capacitors, resistors and inductors, and a package for accommodating them.
Within the existing art, in order to form a high frequency semiconductor device such as a single-stage microwave amplifier, a transistor, which is hermetically sealed to prevent degradation of its characteristics and which is provided with leads to connect to other circuit elements, is mounted on a circuit substrate. The transistor is connected with the other elements which are also mounted on the same circuit substrate and are required for the formation of an amplifier. The circuit substrate is housed in a metal case.
Some of the various elements fixed on the substrate and forming the amplifier, such as transistors, are individually, hermetically sealed and as a result occupy a great deal of space. Thus, a large circuit substrate and an appropriately large case are required in order to mount such an amplifier.
In a situation involving a multi-stage amplifier the size of the total device is quite large because the device consists of a plurality of large, interconnected circuit substrates mounting hermetically sealed containers.
In the existing method for coping with this disadvantage transistor chips are mounted together with the other necessary circuit elements on the substrate formed on the metal base. The transistor chips are not individually hermetically sealed. Rather, all the circuit mounting substrates are accommodated in one metal case which is hermetically sealed. Such a structure has the advantage that physical dimensions are reduced as compared with the existing multi-case structure. However, at the same time it has the disadvantage that perfect sealing becomes difficult because the size of the seal is substantially greater for the entire metal case than for the structures in which individual transistors are hermetically sealed.